| Crynodeb: | <p>Abstract</p> <p>Background</p> <p>The complex responses of plants to DNA damage are incompletely understood and the role of members of the serpin protein family has not been investigated. Serpins are functionally diverse but structurally conserved proteins found in all three domains of life. In animals, most serpins have regulatory functions through potent, irreversible inhibition of specific serine or cysteine proteinases via a unique suicide-substrate mechanism. Plant serpins are also potent proteinase inhibitors, but their physiological roles are largely unknown.</p> <p>Results</p> <p>Six <it>Arabidopsis </it>genes encoding full-length serpins were differentially expressed in developing seedlings and mature tissues. Basal levels of <it>AtSRP2 </it>(At2g14540) and <it>AtSRP3 </it>(At1g64030) transcripts were highest in reproductive tissues. <it>AtSRP2 </it>was induced 5-fold and <it>AtSRP3 </it>100-fold after exposure of seedlings to low concentrations of methyl methanesulfonate (MMS), a model alkylating reagent that causes DNA damage. Homozygous T-DNA insertion mutants <it>atsrp2 </it>and <it>atsrp3 </it>exhibited no differential growth when mutant and wild-type plants were left untreated or exposed to γ-radiation or ultraviolet light. In contrast, <it>atsrp2 </it>and <it>atsrp3 </it>plants exhibited greater root length, leaf number and overall size than wild-type plants when exposed to MMS. Neither of the two serpins was required for meiosis. GFP-AtSRP2 was localized to the nucleus, whereas GFP-AtSRP3 was cytosolic, suggesting that they target different proteinases. Induction of cell cycle- and DNA damage-related genes <it>AtBRCA1</it>, <it>AtBARD1</it>, <it>AtRAD51</it>, <it>AtCYCB1;1 </it>and <it>AtCYCD1;1</it>, but not <it>AtATM</it>, was reduced relative to wild-type in <it>atsrp2 </it>and <it>atsrp3 </it>mutants exposed to MMS.</p> <p>Conclusion</p> <p>Expression of specific serpin genes (<it>AtSRP2 </it>and <it>AtSRP3 </it>in <it>Arabidopsis</it>) is required for normal responses of plants following exposure to alkylating genotoxins such as MMS.</p>
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